Although the present invention is useful in various processes in which a continuous plug, gravity flow of particles is to be contacted by a fluid, it has particular application in the solid state polymerization of polyester, in which the polyester is first formed to a low molecular weight in a melt phase, is solidified, formed into particles, and further polymerized in the solid state to a higher molecular weight.
Many reactor designs employ internal diffusers for introduction of inert gas. These diffusers along with their supports are expensive and may interfere with the uniform flow of pellets through the reactor. In addition, the structural integrity of internal diffusers and supports cannot be guaranteed without a proper understanding of mass flow of solids.
Reactors may also use a sparge ring around the circumference of the vessel either by itself or in combination with internal diffusers. While a sparge ring may avoid interference with pellet flow, it may be expensive to fabricate and if not properly designed offers a place for fines to collect.
U.S. Patents relating to the solid state polymerization of polyester, and reactors for conducting the polymerization, include U.S. Pat. Nos. 4,276,261; 3,405,098; 4,064,112; 3,960,817; 3,544,525 and 3,756,990.